Thought I would contribute..I have a 99 E 350 and two summers ago had a plug blow out. A guy in Vanderhoof did the job..and it was quite a piece of work. Tapping the hole blind..couldn't actually see it. In with the heli-coil.
I had bought a set of coils from Summit Racing some months ago, too..a just in case thing. At a Ford dealer here in Canada they are $100.00 a piece...Summit was..uhmmm...$100? for 10. Anyway...with 210,000 on the clock I decided now is a good time to change out all the plugs and coils...had the work done here in Penticton. $600.00. That included a tire rotation, by request.
Gary Haupt